Over the last few decades the choices of chemical protective clothing and ensembles available to hazardous materials clean up responders and plant workers have expanded significantly. As awareness of the hazards associated with dangerous and toxic chemicals in the liquid and or vapor forms increased, the chemical protective fabrics began to transition from rubber or PVC based fabrics to the more chemical permeation resistant film based fabrics.
ASTM International (ASTM), originally known as the American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, and services. In 1977 the ASTM formed the F23 committee on protective clothing. This committee has issued numerous test standards that have impacted the development of chemical protective clothing. One such standard was ASTM F739 which standardized how chemical permeation through protective fabrics is measured. This standard, which measures chemical migration through the fabric on a molecular level, highlighted the differences between traditional rubber products and newer barrier films. Another standard, ASTM F1001 established a chemical test battery consisting of 15 liquid chemicals and 6 gases representing a broad base of chemical families. If one chooses to document to this standard, all chemicals must be tested and reported. This again highlighted the advantage of high barrier films over the then traditional elastomeric fabrics.
One of the earliest film based fabrics to be developed was Saranex 23 laminated to Tyvek. This thin material offered considerable chemical protection compared to elastomeric products and solved the difficult problem of garment decontamination since this product was designed to be disposed of after use. U.S. Pat. No. 4,833,010 issued in 1989 describes a material that is heat sealable and exhibited greater than 8 hours permeation resistance to all of the ASTM F1001 chemicals. This material was used to fabricate gas tight suits offering the highest level of protection while still being designed for disposal after exposure to chemicals.
In 1986 the National Fire Protection Association (NFPA) established the subcommittee on Hazardous Materials Protective Clothing and Equipment. The first standard issued by this subcommittee was NFPA 1991 issued in 1990. This standard specified performance requirements for a gas tight level A suit that included chemical, physical, and flammability requirements. The film based products up until then offered excellent resistance to chemicals but readily burned and or melted when exposed to flame. To overcome this obstacle, the standard allowed for the wearing of a secondary outer cover typically made from a reflective metalized flame retardant (FR) fabric. The single skin standalone suits to meet the requirements of NFPA 1991 were typically made of composites of fluoropolymers that were expensive and difficult to manufacture. Additionally, these garments offer limited radiant heat resistance as they do not have a reflective surface.
Several attempts have been made at producing a single skin standalone material that offers both chemical and flash fire resistance. U.S. Pat. No. 4,792,480 describes a fabric that contains a reflective layer, a chemical layer, and a fabric substrate. The reflective outer surface is covered with a heat sealable layer of flame retardant film that is radiant heat transparent and light transparent thermoplastic film. There is an inherent problem with making a clear transparent thermoplastic film flame retardant. When flame retardant additives are introduced into the film, the result is marginal FR performance and the film becomes milky or cloudy significantly reducing the ability of the reflective surface beneath it to reflect the radiant heat load. If a non flame retardant clear heat sealable film is used, it will burn off of the surface of the composite when subjected to a vertical flame. There has been no known product in the market based on the '480 patent.
U.S. Pat. No. 5,948,708 describes a fabric containing a reflective outer surface, a flame retardant fiber substrate, and a series of coextruded composite polymer barrier layers on the inner surface next to the wearer's skin. While this fabric provides flame and chemical protection, it is only heat sealable on the inside surface. This means that the seams of a garment made from this composite can only be heat sealed on the inside of the garment next to the skin. Typically the outer seams on the reflective surface are covered with a clear FEP pressure sensitive tape. The clear FEP pressure sensitive tape can be easily removed or abraded from the metalized outer surface of the garment through usage. While the wearer may be protected by the inner seams, undesirable contamination of the fabric substrate could occur through compromised outer seams.
US Publication US2004/0063371A1 describes a spunlaced flame retardant nonwoven fabric laminated to a halogenated flame resistant polymeric film. This laminate offers limited chemical resistance and little or no radiant heat resistance.
US Publication US2005/0255771A1 describes a chemical and flash fire protective fabric comprising a flame retardant fabric inner surface, a chemical barrier layer, and a flame retardant outer polymer layer. The seams formed by the outer flame retardant outer layer are heat sealable. The disadvantage of this fabric is that it does not contain a reflective layer to block the radiant heat load.